1. Field of the Invention
The present invention relates to an improvement in a driving apparatus for driving a moving member, a correction optical apparatus having a correction optical system, or an image blur correction apparatus having the correction optical apparatus.
2. Related Background Art
For an existing camera, since exposure determination, focusing and other operations important for photographing are all automated, even a person unskilled in camera operation has a very little possibility of causing a photographing failure.
Moreover, a system for correcting image blur caused by manual vibration applied to the camera has been recently researched, and factors for inducing photographer's photographing failure have almost been eliminated.
Here, a system for correcting image blur caused by manual vibration will briefly be described.
The manual vibration of the camera during photographing is a vibration having a frequency normally in the range of 1 Hz to 12 Hz. In order to enable a photo with no image blur to be taken even if such manual vibration occurs at the time of releasing a shutter, as a basic idea, camera vibration caused by the manual vibration is detected, and a correction lens has to be displaced in accordance with the detected value. Therefore, in order to enable photos to be taken in such a manner that no image blur occurs even if manual vibration occurs, first, the camera vibration needs to be exactly detected, and secondly, an optical axis change caused by the camera vibration needs to be corrected by displacing the correction lens.
The vibration (camera vibration) can be detected, in principle, by mounting, on the camera, a vibration detection apparatus comprising a vibration detector for detecting acceleration, speed and the like and a calculation portion for electrically or mechanically integrating output signals of the vibration detector to output displacement. Subsequently, by controlling a correction optical apparatus in an image blur correction apparatus mounted to displace a correction optical system based on the detected information and to change a photographing optical axis, image blur correction can be realized.
As a conventional example of driving means of the correction optical system, a driving portion is used in which a coil and a magnet opposed thereto are used, the magnet is disposed on a fixed portion, the coil is disposed on the correction optical system, and an electric current is supplied to the coil for driving. A vertical vibration direction when a camera is set up in a positive position (hereinafter referred to as the pitch direction) and a transverse vibration direction orthogonal to the pitch direction (hereinafter referred to as the yaw direction) are detected, two pairs of the driving portions are correspondingly arranged to correct vibrations in the pitch and yaw directions, and the two directions are driven independently of each other. Such driving means is proposed.
FIG. 9 is a perspective view showing a coil and magnets in an example of a conventional driving means, and FIGS. 10A and 10B are schematic views showing the relationship of the magnets and coil constituting the conventional driving means.
In the drawings, a first magnet 901 is polarized at 901a and 901b, has a central non-magnetized neutral area 901c, and is fixed to a base plate (not shown). In the same manner as the first magnet 901, a second magnet 902 is polarized at 902a, 902b, has a central non-magnetized neutral area 902c, and is fixed to a base plate (not shown). The first, second magnets 901 and 902 are attached to first, second yokes 903 and 904, respectively, to constitute a closed magnetic circuit having a flow of magnetic flux as shown by an arrow B. A flat coil 905 disposed between the opposed first and second magnets 901, 902 is integrally attached to a support frame 907 for supporting a correction optical system 906, and driven in a direction shown by an arrow C by supplied electricity.
Additionally, FIG. 10A shows that the correction optical system 906 is positioned in a driving center, and FIG. 10B shows that the correction optical system 906 is driven by a maximum driving amount in the direction of the arrow C, and positioned in a driving end. Furthermore, a thrust applied to the coil 905 is a product of a magnetic flux density passed through the coil 905, a current supplied to the coil 905 and an effective length of the coil through which the magnetic flux passes. Moreover, the effective length of the coil 905 through which the magnetic flux passes is proportional to a width L.sub.0 in which the coil is opposed to the magnets (of a driving direction of the coil constituted integrally with the correction optical system). Therefore, when a magnetic flux leakage in the closed magnetic circuit is ignored, the thrust applied to the coil is substantially proportional to the width L.sub.0 of the coil opposed to the magnets.